Dynamic Respiratory Tracking In the Presence of Cardiac Motion for Cardioablation
Abstract
Purpose
To investigate internal treatment margins for targets undergoing cardiorespiratory motion with the use of dynamic tracking technology.
Methods
A cardiac phantom was developed using a 3D printed scaffold, Arduino UNO R3, Geckodrive G251 step motor driver, WanTai 42BYGHM809 stepper motor, and the Arduino IDE software, to simulate cardiac motion parallel to motion of a respiratory BrainLAB ExacTrac gating phantom. A small ball bearing was simultaneously used as the target and the internal motion surrogate, with infrared reflectors as an external surrogate. 1D motion data from clinical cardiac magnetic resonance imaging was rescaled to peak-to-peak amplitudes of 3, 6, and 9 mm, used in conjunction with five free-breathing respiratory traces from cardioablation patients, for a total of fifteen dynamic tracking traces. Dynamic tracking delivery was tested using a BrainLAB ExacTrac Vero4DRT linear accelerator, with the internal-external surrogate correlation model built on the combined cardiorespiratory motion. Absolute localization errors of radiation delivery location from the predicted target location was obtained from automated ExacTrac delivery logs. Similar distributions of position discrepancies for hypothetical treatments delivered with no tracking enabled were calculated by convolving the distributions of each cardiac and respiratory trace. Internal target volume (ITV) margins were obtained by calculating the 95th percentile of the localization errors.
Results
Dynamic cardiorespiratory motion tracking consistently reduced ITV margins compared to no tracking across the fifteen distinct traces. Mean ITV margin reduction was 2.3 +/- 1.3 mm. Tracking reduced margins to be within 0.5, 1.0, and 1.5 mm of half the peak-to-peak cardiac motion amplitude for the 3, 6, and 9 mm cases respectively, regardless of respiratory motion amplitude.
Conclusion
This work shows that dynamic tracking can reduce ITV margins for targets affected by cardiorespiratory motion by decreasing the respiratory motion contribution to deviations, minimizing the volume of healthy tissue irradiated.